"Self-deleted" tag and mapping panel

Days ago, after updating Mp3tag to version 3.00, when opening the application I came across a incompatibility warning and that it was necessary to update to 3.01. That's what I did, but then I realized that all the mapping settings I did were gone. I thought it happened because of the two consecutive updates, so I accepted.

Until, days later, I notice that my tag panel returned to an older version that I had edited before ... however, there was no plausible justification for this, since I had not updated or tampered with the files or anything. Again, I ignored and redid the tags.

Today, I went to edit the tags of a song by opening Mp3tag through the Windows context menu, and a warning appears saying "the file cannot be edited because it is corrupted" (which was not true). I went to open Mp3tag and: all the tags in the tag panel are gone. Without justification. I didn't touch the AppData folder or anything.
I would like to know if there is an explanation for these errors and I would like you to correct them. Thanks.

Could it be that you installed MP3tag in a different way, standard instead of portable or vice versa? This would explain the lost settings.
If you changed that then the old settings should still be in the old installation location.
As I use MP3tag without any problems, you would have to supply way more evidence that you really encountered an MP3tag problem instead of a local one.
E.g. how do you know that the file was not corrupted? Did you test it? Which program did you use to do the test? How did the program tell you that everything is ok?
What kind of files are we talking about?
Could you still supply it so that others could have look at it?

As I recall, I always installed it in standard mode, never portable. And it was an mp3 file, which is not corrupted as it can be heard normally.

So it is not quite clear whether you installed in a way that kept the old settings or not.
I would now look for old installation folders of MP3tag and see if you can retrieve some of the old settings.

And as for the file: being playable does not mean that it is not somehow corrupt, esp. as you already get an according message.
Please see the tools linked in this thread and check it:

The installation location (ProgramFilesx86) and the location of the .ini file of tags (AppData / Roaming) are the same, the file is modified.

As for the corruption of the music files I will check later.